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Protecting the butterflies' forest

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Monarch butterflies travel up to 2,800 miles from North America to the Monarch Butterfly Biosphere Reserve in Sierra Chincua, central Mexico, each year in one of the earth's most extraordinary migrations. Tony Avelar/The Christian Science Monitor

Because of a recent drought, the fir forests where the monarchs overwinter have suffered an infestation of bark beetles. Large sections of trees have been cleared in an attempt to control the insects, leaving empty patches on a mountaintop. Tony Avelar/The Christian Science Monitor

Forest conservation and preservation are key to maintaining the population of butterflies. Up to a billion monarchs will migrate to this and other small reserves, and healthy trees are critical to their survival. Tony Avelar/The Christian Science Monitor

Without the trees to house them, the butterflies are threatened by cold winter air and rain. But because of the unnaturally dry year, the bark beetle population has exploded, burrowing in and robbing the trees of nutrients until fir needles turn orange and the trees die. Tony Avelar/The Christian Science Monitor

Rosendo Caro, director of the Monarch Butterfly Biosphere Reserve, talks with scientists about the problem of the bark beetle. This year little rain had fallen by July, and the trees were weakened, making them more susceptible to the beetles. Tony Avelar/The Christian Science Monitor

A scientist gathers larvae of the bark beetle from a dead tree. The insects have long been present in the monarch reserve, usually attacking a few trees in the driest months of early spring, before heavy seasonal rains that normally start in May. Tony Avelar/The Christian Science Monitor

Dr. Rodolfo Campos, right, of the Chapingo Autonomous University, Division of Forestry, and other scientists check a dead tree for the larvae of the bark beetle. Tony Avelar/The Christian Science Monitor

Bark beetle larvae are seen on a sample from a dead tree. Authorities have already identified more than 7,500 infested trees. Currently, they are removing the affected trees from the forest to slow the infestation. Tony Avelar/The Christian Science Monitor

After decades of trying to stop logging in Mexico's monarch butterfly reserve, biologists and park workers have been forced to cut down thousands of fir trees themselves, to combat this unprecedented infestation. The infested bark is buried, and underground cables are used to haul the trees onto trucks. The work is slow, with trees inspected one by one. Tony Avelar/The Christian Science Monitor

When the butterflies arrive to spend the winter huddling in large groups on branches, the tree cutting will have to stop so they won't be disturbed. Monarchs come from as far away as Canada and the United States, covering the trees and even bending branches with their collective weight. Tony Avelar/The Christian Science Monitor